Various endoscopes (which shall be called electronic endoscopes in the present invention) wherein solid state imaging devices, such as charged coupled devices (CCD's ), are used for an imaging means have been recently suggested.
Such an electronic endoscope has advantages in that it has a higher resolving degree than a fiberscope, it can easily record and reproduce picture images and it can easily make picture image processes such as the magnification of picture images and comparison of two picture surfaces.
The above mentioned electronic endoscope is desired to be thin in the insertable part in order to reduce the pain to the patient when it is inserted. However, the outside diameter of this insertable part or particularly of the tip is restricted by the size and shape of a solid state imaging device internally provided in the tip.
In a conventional solid state imaging device, for example, as shown in the specification of U.S. Pat. No. 4,491,865, a solid state imaging chip is secured on a base. On the solid state imaging chip, chip side bonding pads are provided on the periphery of a square or rectangular image area (effective imaging part). On the other hand, on the base side, base side bonding pads (leads) are provided. The above mentioned chip side bonding pads and base side bonding pads are connected respectively with each other through bonding wires or the like. The number of leads provided on the above mentioned base is at least 6 but is generally 14 to 20. For example, respectively 10 of the above mentioned chip side and base side bonding pads are arranged generally along the two opposed sides of the above mentioned image area.
In case the bonding wire is, for example, a general gold (Au) wire or aluminum (Al) wire of 25 .mu.m., the size of the above mentioned chip side bonding pad may be about 0.1 to 0.12 mm. square, the spacing may be about 0.1 mm. and therefore the pitch may be about 0.2 mm. On the other hand, in the above mentioned base side bonding pads, as the base is made of ceramics, glass epoxy or a lead frame, the pitch of the pads must be about 0.635 mm. (1/40 inch). Therefore, whether these base side bonding pads can be laid out at high space efficiency influences the outside diameter of the insertable parts.
However, conventionally, the above mentioned base side bonding pads have been arranged in a row along the side of the imaging chip. Therefore, there are problems that the pitch of the above mentioned base side bonding pads is so large that, particularly, in case there are many leads, the base will become large and, as a result, the insertable part of the electronic endoscope will become thick.
When the chip side bonding pads are provided, along the two sides opposed to each other on the image area, the chip itself will become larger than when they are collected on one side and, as a result, the diameter of the insertable part will become even larger.